Nanotechnology holds great promise as the next industrial revolution and is expect to be a major driving force for the U.S. economic recovery and development. The long-term objective of this project is to enable safe nanotechnology through the understanding of biochemical mechanisms and physicochemical factors influencing the adverse health effects of nanomaterial exposure. This proposal specifically addresses the carcinogenic effects of carbon nanotubes (CNT) following chronic pulmonary exposure. Lung cancer is the leading cause of cancer death, and environmental and occupational exposure is the major cause of most cases. Recent studies have shown that CNT can induce tumors and tumor-associated pathologies, but the underlying mechanisms and key contributing factors are unclear, which limits human risk assessment and disease prevention. We hypothesize that chronic exposure of human lung epithelial cells to CNT induces malignant transformation and carcinogenesis through complex mechanisms that involve p53 dysregulation and induction of cancer stem cells (CSC) and epithelial mesenchymal transition (EMT). We also propose that combination biomarkers that characterize these biological changes could be predictive of CNT-induced carcinogenesis. Three specific aims are proposed. In Aim 1, we will test the requirement of p53 dysregulation in CNT carcinogenesis and determine key physicochemical properties controlling CNT carcinogenicity. Aim 2 will study the role of CSC in CNT carcinogenesis and determine the unique CSC markers for CNT carcinogenic responses. Aim 3 will characterize the EMT network and determine its role in CSC acquisition and CNT carcinogenesis. We will identify combination biomarkers to predict CNT carcinogenesis and validate their pre- clinical use in lung orthotopic xenograft models. Our expectations are that, at the conclusion of this project, we will have determined the biomarkers for CNT carcinogenesis and identified key physicochemical factors determining the carcinogenicity of CNT. This work is important because of the overall impact it will have on risk assessment and prevention of CNT carcinogenesis and development of safe nanotechnology. We expect the impact to be broad since the findings from this project are highly applicable to various nanomaterials. The proposed work is innovative because it combines the novel concepts of CSC and EMT to unveil the underlying mechanisms of CNT-induced carcinogenesis which are largely unknown at present. In addition, the experimental models developed in this project, e.g. chronic exposure and lung orthotopic xenograft models, could be used as predictive screening tools for carcinogenicity testing of nanomaterials which are currently lacking and greatly needed.